Softeners for synthetic rubber



' ricerca oa. 24, 1944 nonna v. subacncuyanora rullo,` omo, uf signor to The B.VF. Goodrich Company, New A York, N. Y., a corporation of New York No Drawing. Application September 12, liliA Serial No. 1410,593

s claims. (a. zoo- 36) This invention relates to a new class of softeners for synthetic rubber and to the improved compositions obtainable by the use of suchsofteners.

In comparison to natural rubber, synthetic rubber is relatively hard, dry and non-tackyand, unlike natural rubber, is incapable of being masticated to a soft plastic condition in which it may I readily be compounded and processed. Accordingly, it is necessary to employ softeners or plasticizers in order to improve its compounding and processing characteristics. The selection of suitable softeners for synthetic rubber has however presented numerous diiculties, particularly in the case oi synthetic rubber of the type prepared by the copolymerization of a butadiene-1,3 hyd'rocarbon and an 'acrylic nitrile. These dimculties are accentuated by the i'act that many softeners ordinarily employed in rubbery or resinous materials are incompatible with this and other types of synthetic rubber and by the further fact that softeners for one type of synthetic rubber do not in all cases function similarly in other types of synthetic rubber. -Even varying the proportions of the monomers in the mixtures employed to form copolymers often necessitates the search for new softeners for the synthetic rubber product. -Aside from these diiiiculties some 'softeners which are compatible with synthetic rubber so adversely aect the properties of vul canizates prepared from compositions containing them as to preclude their use.

I have now discovered that benzyl alcohol and its alkyl ethers are extremely edective softeners for any of the synthetic rubbers prepared by the polymerization of a butadiene-1,3 hydrocarbon either alone or in s. 1w: with otherpoly wherein R is hydrogen or an-alkyl group. .Compounds in which R is hydrogen or an alkyl group containing less than ten carbonatoms are ordinarily employed in this invention, benzyl alcohol and benzyl amyl ether being particularly eiective softeners.

As mentioned hereinabove these softeners may be used with synthetic rubber` prepared by the polymerization of a butadiene hydrocarbon, by which is meant butadiene-1,3 and its homologs which polymerize in essentially the ysaine ner such as isoprene, 2-3 dimethyl butadiene-1,3

piperylene and the like, either alone or in ad- Vmixture with each other or with other unsaturated monomers copolymerizable therewith.

Among such unsaturated monomers copolymeriz'able with a butadiene hydrocarbon to form synthetic rubber there may be mentioned, the aryl olefins such as styrene and vinyl naphthalene,l the acrylic acids, esters, nitriles and amides such. as acrylic acid, metml acrylate, methyl methacrylate, acrylonitrile, thacrylonitrile, methacrylamide and the iaobutylene, methyl vinyl ether, methyl vinyl ketone, vinylidene chloride and other unsaturated hydrocarbons, esters, alcohols, acids, ether-s, etc., which contain the nolimerizable structure where at least one of the disconnected valencies dietry-or polar character of the molecule.

merizable compounds. When such compounds l are incorporated in synthetic rubber extremely soft plastic compositions which also possess good tackiness and which may be cured to valuable synthetic rubber vulc y .'*tes are obtained. Ac-

cordingly this invention comprises both vulcan ized and unvulcanized synthetic rubber compositions r:.': y as a softener, benzyl alcohol or an allwl ether thereof.-

In dition to nzyl alcohol itself such alkyl ethers oi benzyl alcohol as benzyl methyl ether, l

. benzyl ethyl ether, benzyl isopropyl ether, benzyl n-propyl ether, benzyl n-butyl ether, benzyl amyl ether, benzyl isoamyl ether, benzyl hexyl ether, benzyl, 2-ether hexyl-ether and the like may be' employed softeners in this invention.. All these the general structure The polymerization to form a synthetic rubbermay be accomplished by any ofthe well hown methods such as polymerization in aqueous emulsion, homogenous polymerization, etc.

The incorporation of the softener with the syn- 4 .thetic rubber may be eiected by any desired method as by adding the softener to synthetic rubber while the latter is being worked on a roll mill, masticating a mixture of the rubber and' softener in an internal mixer such as a Banbury type mixer, adding the softener to an emulsion or dispersion of. the synthetic rubber or by adding the softener to a solution of the rubber in a l solvent.

The amount of the softener added will dependl somewhat 4upon the properties desiredin the composition and upon the nature of the rubber treated.' the rubber and the softener being compatible over a wide range of proportions. Inl commercial operations it -will' ordinarily be'expedient to employ rom about 5 to Weiht'of the softener for' e 100;

5.0.parts byl thetic rubber but mounts smaller or larger than this ransing from 1 to 100 parts of softener for 100 parts synthetic rubber are also effective. With synthetic rubber prepared by the copolymerization of butadiene and styrene or of butadiene and acrylic esters it is possible to use smaller amounts vof softener than are required with rubber prepared by the copolymerization of butadiene and an arcylic nitrlle.

In a specific example of 'this invention a softened synthetic rubber composition is prepared by incorporating on a roll mill 50 parts by weight of benzyl alcohol in 100 parte by 4weight of a synthetic rubber prepared by copolymerizing butadiene and acrylonitrile. The softener adds easily producing an extremely soft gum with excellent tack. The conventional compounding and vulcanizing ingredients including carbon black and sulfur are then dispersed in the softened composition to produce a plastic, tacky, easily processed compound which is then vulcanized to an excellent vulcanizate. The vulcanizate possesses an exceptionally good rebound elasticity and a low permanent set. Moreover the vulcanizate remains substantially unaffected by pro- 25 longed immersion in mineral oils.

When on1y'10 parts of benzyl alcohol are similarly incorporated in 100 parts of a synthetic rubber prepared by the copolymerization of butadiene and styrene, a soft, plastic, easily processed stock is obtained. The stock is much softer and more plastic than a heat softened butadiene styrene copolymer and is even much softer than stocks obtained by the addition of such softeners as pine tar, coal tar or album phthalate. 'rms softened 'composition may also be compounded and vulcanized inthe usual manner to yield `excellent vulcanizates.

In another embodiment of this invention 50 parts by weight of benzyl amyl ether are incorpcrated in 100 parts by weight of a butadiene `acrylonltrile copolymer as described above.

that the invention be limited solely thereto for many. modifications and variations will be apparent to those skilled in the art. For example, other materials auch as natural rubber, other softeners, pigments, fillers, `vulcanizinir agents, accelerators, antioxidants and the like may .be

included in the compositions herein described without departing from the spirit and scope of the invention as defined in the appended t I claim: v.

l. A composition of matter comprising a synthetic rubber prepared by the polymerization of a butadiene-1,3 hydrocarbon and, as a softener therefor, a member of the class consisting of 10 benzyl alcohol and alkyl ethers of benzylalcohol wherein the alkyl group contains less than ten carbon atoms.

2. A composition offinatter comprising a synthetic rubber prepareclkluy the copolymerization l5 of a butadiene-1,3 hydrocarbon andvat least one other" unsaturated compound which contains a 20 group and is coplymeri'zable'therewith, and, as

a. softener therefor, amember of the class conisisting o`f benzyl alcohol and alkyl ethers of benzyl alcohol wherein the alkyl group contains less than ten carbon atoms.

` 3. A compositie fof matter comprising a. synthetic rubber prepared by copolymerizing butadiene-1,3 and` acrylonitriie and,A as a softener Atherefor, a member of the class consisting of` benzyl alcohol and alkyl ethers of benzyl alcohol 30 wherein the alkyl group contains less than ten carbon atoms.

4. A composition of matter comprising a synthetic rubber prepared by copolymerizing butadiene-1,3 and styrene and, as a softener therefor, 5 a member of the class consisting of benzyl alcohol and alkyl ethers of benzyl alcohol wherein the alkyl group contains less thanten carbon atoms.

. 5. The composition of claim 3 wherein the softener is benzyl alcoh l.

o 6.7The composition f claim 4 wherein the `softener is benzyl alcohol.

'7. The composition 4'of claim 3 wherein. the softener is benzyl amyl ether.

' 8.' synthetic rubber composition prepared by vulcanizing a copolymer of a butadiene-1,3 hydrocarbon and at least onev other unsaturated compound which contains a 5 group ,and is copolymerizable therewith in the presence of 'a compound of the class consisting of benzyl alcohol and alkyl ethers of benzyl alcohol wherein the alhvl group contains less than ten u carbon atoms.

DONALD V. BARBACH. f

l K CERTIFICATE CE CORRECTION. Patent No., 2,560,897., october 2h, 19ML. Y DONALD v. sARBAcH.

of the above numbered patent'r'eq-i-ring correction as follows: Page l, first Patent should be read with. this Acozvrection therein that the same may ConformA to the record of the case in the Patent 0.151106.,

signed and sealed this 50i-.h vmay ofJlanuary, A. D. 19u5.

Leslie Frazer `(Seal) Acting Commissioner of Patents.. 

